This invention relates to an input device and, in particular, to an input device located on the surface of a display such as a liquid crystal display device (LCD), cathode ray terminal (CRT), and the like.
A typical input device is used to connect the display electrodes on the inner surface of the display substrates across a seal at the periphery of the display area of the display device to a drive circuit. A conventional input device 20 for a liquid crystal display device is shown in FIG. 1. Display device 20 includes an upper high-molecular weight resin film substrate 21 and an opposed lower glass substrate 22. Transparent electrodes 23 and 24, typically made of a film such as indium tin oxide (ITO), SnO.sub.2, or other inorganic compounds, are disposed on resin film substrate 21 and glass substrate 22, respectively. Transparent electrodes 23 and 24 may be arranged as perpendicularly-oriented lines with respect to each other, or they may be formed in any other desired pattern. Substrates 21 and 22 are separated a predetermined distance from each other by spacers 25 and a seal member 26 about the periphery of the display area.
A flexible connecting member 27, which may be made of connecting wiring on a flexible printed circuit 31, connects an input power source to transparent electrode 23. In the most simple configuration (not shown), substrate 21 would extend beyond seal member 26 and electrode 23 would project beyond seal member 6 to contact flexible connecting member 27 to a conductive adhesive layer. Unfortunately, substrate 21 is made of an organic material, unlike glass substrate 22 and inorganic electrodes 23 and 24. Since the bonding of the inorganic electrode to the organic substrate is less secure than the bonding of two inorganic materials, it is more likely that an inorganic electrode will detach from organic resin film substrate 21 than from inorganic glass substrate 22. Accordingly, if flexible connecting member 27 was directly connected to electrode 23 with only a conductive adhesive layer between them, and flexible connecting member 27 was accidentally pulled, it is more likely that electrode 23 would disengage from substrate 21 than if flexible connecting member 27 was attached to an electrode connected to glass substrate 22.
In view of this, conventional input device 20, as shown in FIG. 1, is utilized to connect flexible connecting member 27 to electrode 23 indirectly, thereby reducing the chance that electrode 23 will detach from substrate 21. Instead of having electrode 23 extend beyond seal member 26, a relay electrode 28 is formed on glass substrate 22 which extends on substrate 22 from a position inside of seal member 26 to the outside. Relay electrode 28 is electrically connected to electrode 23 by a conductive adhesive layer 29, and to flexible connecting member 27 by a conductive adhesive layer 30. The advantage of input device 20 is that if flexible connecting member 27 is accidentally pulled, relay electrode 28 which is made of an inorganic material will more likely remain attached to inorganic glass substrate 22 than to organic substrate 21. In theory there is no force which would separate electrode 23 from substrate 21.
Conventional input device 20 is less than fully satisfactory in practice. This is due to the fact that film substrate 21 shrinks during production, because of the high production temperatures necessary in the heat pressing step, and later expands after cooling. Since electrode 23, conductive adhesive layer 30 and relay electrode 28 do not have the same shrinkage rate, undesirable stresses occur between relay electrode 28 and film substrate 21 which tend to cause cracks in electrode 23. This causes electrode 23 to peel from film substrate 21, or can cause conductive adhering layer 29 to peel from electrode 23.
Accordingly, the present inventors have improved the electrical connection of conductive adhesive agent 29 by including a conductive synthetic resin 40 disposed between electrode 34 on substrate 30 and conductive adhesive agent 29 as shown in FIG. 5. This improvement is the subject of the present invention, and is discussed in more detail below. To further eliminate peeling of electrode 23 from resin film substrate 21, the present inventors modified the traditional continuous seal 26 shown in FIG. 1 into forms for providing more support. In one attempt, seal 26 was modified into the continuous seal 126 shown in FIGS. 2 and 3 to include rectangular shape segment 127 which extends around and isolates conductive adhering layer 29 to support electrode 23 against film substrate 30. However, this configuration resulted in several disadvantages in that electrode 23 which passes through the inside circumference of continuous seal 26 is subject to strong bending stressed which can result in a crack 34. Formation of crack 34 raises the resistance of electrode 23 at the particular location and, as a result, decreases the strength of the signal which is input to the rest of electrodes 23. As will be discussed in further detail below, the inventors herein have resolved this cracking problem by making seal 127 discontinuous at the juncture between the electrode and substrate as shown in FIG. 16.
Efforts to eliminate cracking has included eliminating a portion of seal member 26 which runs across electrode 23 as shown in FIG. 4. However, in this case there is insufficient sealing material to seal substrates 21 and 23. Conductive adhesive agent 29 tends to peel from electrode 23 as substrate 21 is deformed during fabrication. This causes an inferior input to electrode 23.
In an input device wherein electrode 23 is formed only on substrate 21 directly and the display functions as an input device for digitizer-like use for line picture inputting on the input surface, the force of a pen or fingers at time of inputting is applied directly to the electrode. In this case electrode 21 on substrate 23 contacts electrode 24 on substrate 23 causing the display to degenerate.
Accordingly, it is desirable to provide a new input device having a conductive synthetic resin disposed between the electrode on the substrate and the conductive adhesive agent which eliminates the peeling of the electrode of the prior art. Additionally, it is desirable to provide a seal configuration to this new input device which will also help prevent electrode peeling but which will not cause bending stresses and cracks in the electrode.